This invention relates to an improved stripping and terminating technique for flat cable. More particularly, it relates to an improved technique for stripping the jacket from multi-conductor flat telephone cable, enabling gang termination to a standard telephone connector.
Telephone hand sets in business offices are normally connected to a distribution box by means of 25 pair band marked distribution (BMD) cable. This BMD cable consists of twisted pairs of individually insulated wires, each pair having a tip and ring conductor. The cable jacket is round and the individual pairs are distinguished from one another by color coding. There are at least two major problems in the use of this BMD cable in a business office. One is that the BMD cable is cumbersome, that is, it is rather thick, and normally lies across the floor rather than being placed under the carpet in the office. The other problem arises in terminating the BMD cable to a connector such as the 25 pair Champ made by AMP, Inc. or the Blue Ribbon made by the Amphenol Company. Each wire of the BMD cable must be identified by its color coding and placed by hand into an individual termination slot in the connector, which is a very tedious and costly procedure. Some of the problems of the bulky, cumbersome BMD cable have been solved by the recent development of a flat cable having multi-pair coplaner conductors, which are particularly adapted to be placed under carpets in business offices. This flat cable is further adapted to be mass terminated rather than having individual wires hand-terminated. The above-mentioned flat cable is described and claimed in U.S. Pat. No. 4,155,613 issued May 22, 1979, titled Multi-Pair Flat Telephone Cable with Improved Characteristics, and assigned to Akzona Incorporated, the assignee of the present invention.
The cable described in U.S. Pat. No. 4,155,613 utilizes a jacket made from a mixture of a plastic and electrically conductive carbon black forming a semi-conductive material. By using this semi-conductive material as a jacket for flat cable, cross talk between pairs of conductors is substantially reduced. This flat cable has at least as good or better cross-talk characteristics as the BMD cable. And, of course, the cross-talk characteristics of the above-mentioned flat cable is much better than cross-talk characteristics of an ordinary flat cable which does not have the semi-conductive jacket. A cross-section of the cable described and claimed in U.S. Pat. No. 4,155,613, May 22, 1979, is shown in FIG. 1.
FIG. 1 shows cable 1 having a plurality of pairs 2 of insulated conductors. Insulation 3 about each conductor may be a known electrical insulation material such as polypropylene. The jacket 4 which surrounds each pair in the cable includes a mixture of an electrically conductive carbon black and a plastic such as polyvinylchloride. The jacket is thus made electrically semi-conductive. There is also provided an insulation sheathing 5, which may be Mylar. By the use of this semi-conductive plastic material as a cross-talk reduction jacket, most of the problems associated with BMD cable, as well as ordinary flat cable, particularly those regarding the bulkiness of the BMD cable and poor cross-talk qualities of ordinary flat cable have been solved.
However, particular problems have come up regarding the stripping of this semi-conductive jacket and mass terminating the cable to a connector. Most of these problems are due to the fact that the jacket 4 itself conducts electricity. By using ordinary cable stripping techniques such as abrasion, the insulation 3 around the individual conductors, as well as the jacket, may be stripped off, thus permitting the conductive plastic 4 to come in contact with conductors 6. This contact could cause short circuits in the cable. Furthermore, in telephone applications where each pair includes a tip conductor 9 and a ring conductor 10, in order to utilize a known termination tool such as the AMP Champ Cable to Connector tool, also known as MI-1, and which is shown in FIG. 8, it is necessary to place the tip conductors on one side 7 of the tool and the ring conductors on the other side 8 of the tool. That is, the tip and ring conductors must be moved to separate planes in order to terminate them. If this separation and termination must be done for each individual conductor by hand, many of the advantages of using flat cable would be lost.
It is believed that applicant has solved the above problems in his invention set forth below.